The subject matter of the present invention relates generally to fuel vent apparatus for venting gaseous fuel vapors from a fuel tank, and in particular to such a vent apparatus which also includes an improved gravity operated valve to prevent liquid fuel spillage from the tank. The fuel vent apparatus of the present invention is especially useful on the fuel tanks of trucks and other vehicles operated by liquid fuel such as gasoline, diesel fuel and the like. However, it is also useful on fuel tanks for outboard motor boats, lawn mowers, chain saws and gasoline cans to prevent fuel spillage and fires when such fuel tanks are accidentally overturned.
Previously, it has been proposed to provide a fuel tank with a fuel filler cap having a gravity operated valve which closes a vent passage in such cap when the tank overturns, as on an outboard motor for a boat discussed in U.S. Pat. No. 1,683,338 of Evinrude, granted Sept. 4, 1928. In addition, it is also known to provide such a filler cap with pressure relief valves to prevent excessive positive pressure in addition to such gravity operated valves on the fuel tank of a motor vehicle, as shown in U.S. Pat. No. 3,757,987 of Marshall, granted Sept. 11, 1973, and U.S. Pat. No. 3,918,606 of Keller, granted Nov. 11, 1975. However, the gravity operated valves employed in such patents all employ a valve control means having a spherical weight which is positioned below the movable valve member and rolls up a guide to urge such valve member into a closed position when the tank overturns. This has the disadvantage that tipping of the gas tank through a much greater angle is required before the gravity operated valves of such prior art apparatus close completely. As a result, these valves are slow acting and do not eliminate spillage under certain conditions.
In the fuel vent apparatus of the present invention, the gravity operated valve is controlled by a plumb weight supported above the movable valve member. This plumb weight control means is much more sensitive in that it closes such valve with very little movement of the tank through an angle of about 30.degree.. Thus, in one embodiment when the axis of the vent body moves from its normal vertical position through an angle greater than 28.degree. in any direction, the gravity operated valve closes to prevent fuel spillage from the tank.
In addition, the present fuel vent apparatus also includes a gas pressure check valve in a second path in parallel with the path through the gravity operated valve. This check valve prevents a vacuum from being created within the fuel tank when the fuel therein is used up, which would otherwise tend to hold the gravity operated valve closed. The check valve opens when a negative pressure is created in the fuel tank and immediately closes as soon as the pressure within the tank is equalized to atmospheric pressure and thereafter becomes slightly positive, preventing spillage when the tank has been tipped on its side. Excess positive pressure within the tank in its tipped position is relieved by the conventional pressure relief valves used on filler caps.